1. Field of the Invention
This invention relates to an image dta converter and a method of converting image data therewith, used in constructing an electronic file system which performs image editing, such as image scaling up/down, area extraction and the like, of image data inputted by a scanner and the like, and permits the edited images to be registered and retrieved as image files.
2. Description of the Related Art
Conventional electronic file systems register image data inputted by a scanner and the like as image files in a file memory in a form converted into compressed data for reducing the amount of the data and, where image editing and an image display are intended, are adapted to restore in advance the entire image to bit image data.
FIG. 10 shows one arrangement of the conventional electronic file systems. In this figure, image data supplied from a scanner 1 through scanning of a manuscript are sent to a compression section 2 via a data switch 8, and compression-encoded in the compression section 2, and the compression-encoded data are stored in a compressed data memory 4. As a compression-encoding method, a variable-length MH (Modified Huffman) encoding method with high compression efficiency is commonly used. As shown in FIG. 11, compressed data memory 4 is packed with an aggregate of the compressed data C.sub.1, C.sub.2, . . . , C.sub.n corresponding to the respective lines in the form of 16 bits a word. A compression code EOP denotes an ending code. An expansion section 3 converts the contents of compressed data memory 4 into bit image data in order from the heading adress, and stores them in an image memory 5. An image editing section 7 registers the contents of compressed data memory 4 in a file memory 6 or retrieves necessary files from the file memory 6 to transfer them to compressed data memory 4. Moreover, when image editing such as image scaling up/down, area extraction and the like, and an image display are intended to be performed, the bit image data of the entire image must be stored in image memory 5 in advance. The contents of image memory 5 after the editing are displayed on a display section 9, and also converted into compressed data through data switch 8 and compression section 2 and the compressed data are stored in compressed data memory 4 and thereafter registered in file memory 6.
In the prior art, in performing the editing and display of the image, the compressed data must be always decoded in expansion section 3 in order from the heading address of compressed-data memory 4 so as to detect the top of every line in the compressed data memory 4. This results in poor operability because of the lengthened processing time. For this reason, with the entire image previously converted into bit image data being stored in image memory 5, and display of the image are performed for image memory 5. In this case, however, a large scale image memory for storing the bit image data of the entire image is required, disadvantageously causing the resultant system to be expensive.